1. Technical Field of the Invention
The present invention relates generally to heating systems for electrically powered smoking articles and more particularly to inductive heating systems for electrically powered smoking articles.
2. Discussion of the Related Art
Previously known more conventional smoking devices deliver flavor and aroma to the user as a result of combustion. A mass of combustible material, primarily tobacco, is combusted and adjacent portion of material is pyrolized as the result of applied heat drawn therethrough, with typical combustion temperatures in a more conventional cigarette being in excess of 800.degree. C. during puffing. During this heating, inefficient oxidation of the combustible material takes place and yields various distillation and pyrolysis products. As these products are drawn through the body of the smoking device toward the mouth of the user, they cool and condense to form an aerosol or vapor which gives the consumer the flavor and aroma associated with smoking.
Conventional cigarettes have various perceived drawbacks associated with them. Among them is the production of sidestream smoke during smoldering between puffs, which may be objectionable to some non-smokers. Also, once lit, they must be fully consumed or be discarded. Relighting a conventional cigarette is possible but is usually an unattractive prospect for subjective reasons (flavor, taste, odor) to a discerning smoker.
A prior alternative to the more conventional cigarettes include those in which the combustible material itself does not directly provide the flavorants to the aerosol inhaled by the smoker. In these smoking articles, a combustible heating element, typically carbonaceous in nature, is combusted to heat air as it is drawn over the heating element and through a zone which contains heat-activated elements that release a flavored aerosol. While this type of smoking device produces little or no sidestream smoke, it still generates products of combustion, and once lit it is not adapted to be snuffed for future use in the conventional sense.
Commonly assigned U.S. Pat. Nos. 5,093,894; 5,225,498; 5,060,671 and 5,095,921 disclose various heating elements and flavor generating articles which significantly reduce sidestream smoke while permitting the smoker to selectively suspend and reinitiate smoking. However, the cigarette articles disclosed in these patents are not very durable and may collapse, tear or break from extended or heavy handling. In certain circumstances, these prior cigarette articles may crush as they are inserted into the electric lighters. Once they are smoked, they are even weaker and may tear or break as they are removed from the lighter.
U.S. patent application Ser. No. 08/118,665, filed Sep. 10, 1993, describes an electrical smoking system including a novel electrically powered lighter and novel cigarette that is adapted to cooperate with the lighter. The preferred embodiment of the lighter includes a plurality of metallic sinusoidal heaters disposed in a configuration that receives, via insertion, a tobacco rod portion of the cigarette.
The preferred embodiment of the cigarette of Ser. No. 08/118,665 preferably comprises a tobacco-laden tubular carrier, cigarette paper overwrapped about the tubular carrier, an arrangement of flow-through filter plugs at a mouthpiece end of the carrier and a filter plug at the opposite (distal) end of the carrier, which preferably limits air flow axially through the cigarette. The cigarette and the lighter are configured such that when the cigarette is inserted into the lighter and as individual heaters are activated for each puff, localized charring occurs at spots about the cigarette in the locality where each heater was bearing against the cigarette. Once all the heaters have been activated, these charred spots are closely spaced from one another and encircle a central portion of the carrier portion of the cigarette. Depending on the maximum temperatures and total energies delivered at the heaters, the charred spots manifest more than mere discolorations of the cigarette paper. In most applications, the charring will create at least minute breaks in the cigarette paper and the underlying carrier material, which breaks tends to mechanically weaken the cigarette. For the cigarette to be withdrawn from the lighter, the charred spots must be at least partially slid past the heaters. In aggravated circumstances, such as when the cigarette is wet or toyed with or twisted, the cigarette may be prone to break or leave pieces upon its withdrawal from the lighter. Pieces left in the lighter fixture can interfere with the proper operation of the lighter and/or deliver an off-taste to the smoke of the next cigarette. If the cigarette breaks in two while being withdrawn, the smoker may be faced not only with the frustration of failed cigarette product, but also with the prospect of clearing debris from a clogged lighter before he or she can enjoy another cigarette.
The preferred embodiment of the cigarette of Ser. No. 08/118,665 is essentially a hollow tube between the filter plugs at the mouthpiece end of the cigarette and the plug at the distal end. This construction is believed to elevate delivery to the smoker by providing sufficient space into which aerosol can evolve off the carrier with minimal impingement and condensation of the aerosol on any nearby surfaces. However, the hollow construction is susceptible to being bent or folded, crushed, collapsed and/or torn through handling. The structure also is vulnerable to damage during cigarette making and packing, particularly in modern, high speed cigarette making and packing machines.
It is desirable to reduce or eliminate the need for contact between the tobacco flavor medium, and any associated structure, and relatively fragile heating elements to minimize disruption or termination of the heating system as the numerous tobacco medium products are inserted, adjusted during use, and removed. It is also important to provide uniform heat for successive firings of a smoking article. Also, heating systems which require thermal contact or close thermal registry between heater elements and the tobacco flavor medium necessitate precise manufacturing tolerances which may be difficult or economically unfeasible to achieve and/or maintain at high mass production rates. In addition, it is always desirable to improve the heating efficiency of heating systems, thereby reducing power consumption of the smoking article and the mass of the power source. Further, conductive and/or convective heating of a tobacco flavor medium wrapped in paper or embedded in a paper matrix necessitates burning through the paper, releasing paper-derived vapors in addition to desired aerosols from the tobacco flavor medium, which could condense on relatively cooler components such as sensitive electronics, causing shorts or other undesired degradations and/or malfunctions.
Commonly owned U.S. Pat. No. 5,060,171, issued Oct. 29, 1991, at col. 10, lines 1-7, discloses coupling energy to a flavor generating article by magnetic or electromagnetic induction followed by suitable recertification and conditioning prior to charging a capacitor which powers the heater.